Update Texture for CSFML's sRGB Support

[DemoXinMC]

Addresses #222

• Updated Texture's constructors with an optional parameter named "sRGB" which selects between the sRGB and non-sRGB versions of sfTexture_create*
• Allows Texture(byte[]) to specify a portion of the passed bytes to use for the new Texture, consistent with other existing constructors